A carved tramp art plaque by Michael Lavery marks the 40th anniversary of the Time and Space Limited Warehouse sign in Hudson Tuesday April 2, 2013. (John Carl D'Annibale / Times Union)

A carved tramp art plaque by Michael Lavery marks the 40th...

Detail from the "Avoidance & Peculiar" exhibit in the north gallery at theTime and Space Limited Warehouse in Hudson Tuesday April 2, 2013. TSL is celebrating its 40th anniversary this year. (John Carl D'Annibale / Times Union)

Detail from the "Avoidance & Peculiar" exhibit in the north...

New construction in the east gallery at theTime and Space Limited Warehouse in Hudson Tuesday April 2, 2013. TSL is celebrating its 40th anniversary this year. (John Carl D'Annibale / Times Union)

New construction in the east gallery at theTime and Space Limited...

The 100 seat theater and cinema at theTime and Space Limited Warehouse in Hudson Tuesday April 2, 2013. TSL is celebrating its 40th anniversary this year. (John Carl D'Annibale / Times Union)

The 100 seat theater and cinema at theTime and Space Limited...

Linda Mussmann, left, and Claudia Bruce, co-founders and directors inside the workshop at their Time and Space Limited Warehouse in Hudson Tuesday April 2, 2013. TSL is celebrating its 40th anniversary this year. (John Carl D'Annibale / Times Union)

Linda Mussmann, left, and Claudia Bruce, co-founders and directors...

Claudia Bruce, left, and Linda Mussmann, co-founders and directors of the Time and Space Limited Warehouse in Hudson Tuesday April 2, 2013. TSL is celebrating its 40th anniversary this year. (John Carl D'Annibale / Times Union)

Claudia Bruce, left, and Linda Mussmann, co-founders and directors...

Time and Space Limited Warehouse in Hudson Tuesday April 2, 2013. TSL is celebrating its 40th anniversary this year. (John Carl D'Annibale / Times Union)

"Avoidance & Peculiar" exhibit in the north gallery at theTime and Space Limited Warehouse in Hudson Tuesday April 2, 2013. TSL is celebrating its 40th anniversary this year. (John Carl D'Annibale / Times Union)

"Avoidance & Peculiar" exhibit in the north gallery at theTime...

Linda Mussmann, left, and Claudia Bruce, co-founders and directors in the "Avoidance &amp Peculiar" exhibit at their Time and Space Limited Warehouse in Hudson Tuesday April 2, 2013. TSL is celebrating its 40th anniversary this year. (John Carl D'Annibale / Times Union)

Linda Mussmann and Claudia Bruce went looking for it recently — their old digs on 22nd Street in Manhattan, between Sixth and Seventh avenues. It was one of those windowed storefronts with an accordion gate, the kind you see everywhere hawking everything from cameras to spandex. In their case, it hawked art. Radical art. Art that questioned, probed, provoked.

But they couldn't find it. The neighborhood had changed too much and gentrified too cleanly in the decades since Mussmann and Bruce — the unified, unifying force behind Time & Space Limited — moved their operations north from New York City to a warehouse in Hudson.

"We couldn't remember where it was," recalls Mussmann, chatting in the TSL office on Columbia Street.

Well, it's been a long time. Around 20 years.

"But we were there a long time," Bruce pipes in. Around 20 years.

When Mussmann founded TSL in 1973, she was an innovative theater director and writer with Brecht, Pinter and Beckett under her belt. In 1976, she met Bruce — an actor with wide, clear eyes and a compatible creative mindset. They fell in love and went to work, collaborating at the storefront on plays that tested boundaries and challenged form.

In the early 1980s they bought a home in rural Columbia County. A few years later, they started shopping around for a new space to house their artistic and theatrical ventures, and they landed — for $150,000 — an empty bakery warehouse. In 1993, TSL Hudson opened at last, not so much born as built with pluck and bailing wire.

Since then, the cavernous downtown presence has hosted innumerous theater pieces, installations, concerts, art-house movies, live-streamed operas, camps, community programs, conversations and events that bend and blend assorted genres. In 40 years, from Manhattan to Hudson, they've done towering maps of the wartime dead ("Home.Land.Grief"); works with found objects; new plays and re-jiggered classics, borne of Mussmann's "20th or 21st century postmodern, sausage grinder kind of mind that I have," with fresh views on Lincoln (Mary Todd), Mary Surratt, "Moby-Dick," "Hamlet," "Macbeth" (from Lady M's perspective) and Napoleon ("War & Peace," complete with Bruce in feather boa); and a crowd sourcing effort to identify portraits of young Hudson men drafted for World War II.

On Saturday, they'll celebrate all of it with "TSL: The First 40 Years," a birthday bash and retrospective of four straight decades of art making.

As Bruce and Mussmann bat their memories back and forth across a tiny office, what becomes clear is that a conversation with one is a conversation with both: Their lives have been so closely intertwined, for so long, in so many capacities of work and life, that they form an inextricably fused artistic unit.

Bruce grew up in Georgia; Mussmann in Indiana. Bruce wears a scarf. Mussmann a bow tie. Bruce is always chilly, Mussmann always warm. But when they finish each other's sentences, it sounds less like interruption than the product of twin mouths tapping the same deep well of art and experience.

They walk through TSL's back gallery, where a project from the '80s ("Avoidance and Peculiar") mixes text with circular saw blades and a deconstructed upright piano that Mussmann describes as an "homage to John" — meaning Cage, the composer, who attended their New York shows.

Then they take a pass through Mussmann's workshop, a fecund mess chock full with the essentials: Tools. Duct tape. The aforementioned bailing wire, which Mussmann calls "the key to survival" and once got them to a Texas gas station when their muffler fell off.

The actor F. Murray Abraham, an old friend and frequent contributor to TSL, describes the pair as "fearless," Mussmann as "a genius" and Bruce as "absolutely the greatest actress I've ever worked with, and I've worked with some pretty extraordinary people."

He isn't throwing around such terms lightly, he says. "The fact is that it's hard to connect with something that really excites you, that titillates you, tingles and just thrills — and that's what their work was, because it was so -out there," he says, recalling an early piece with multiple salvaged windows outfitted with text and lights made from tin cans. Abraham and Bruce took turns walking to the windows and reading what they found there. "And my daughter, who was about 10 at the time, in middle of one of the long pauses, in her clear, piercing, bright voice said, 'IS THIS A PLAY, OR WHAT?'"

The cans came from New York pizza shops, Mussmann says — red sauce. There are still a few of those in the workshop, too. Long ago, Mussmann learned to make sets small enough to fit Bruce's VW van, which is how they met: Mussmann needed someone to schlep stuff around. In the same spirit of pragmatism, they moved their home from a rural pocket near Ancram to the north end of Hudson, a working-class neighborhood on the other side of the tracks. Or, more accurately, the truck route.

But this struggling industrial burgh has undergone a transformation since then, luring artists, hipsters and antiquing downstaters to its shops and galleries on Warren Street and the Helsinki Hudson music club on Columbia. If the city has any footing on the cutting edge, it has Mussmann and Bruce to thank for it. "It's changed so much since we were here," Bruce says. "And you know, we have been part of that change. We were pioneers here." Mussmann remembers the first time abstract painter Ellsworth Kelly wandered in, for a screening of Jean-Luc Godard's "Contempt." "We were doing his favorite filmmaker. He came in, and he's like, 'Oh, what is this place?'"

In the early 2000s, Mussmann became active in a push against a new cement plant, and she's run for mayor four times — most recently in 2011, the same year she and Bruce were married in a midnight ceremony that gave them fair claim to the title of first gay couple legally wed in New York state.

What drives their art is no mystery to those around them. "Their long-term loving relationship, and this thing that they've built, is quite extraordinary," says Judy Grunberg, a Chatham artist and TSL board member. Adds Abraham: "It's the power of love. There's not a doubt in my mind. And anyone who meets them sees that — and that's power."

They aren't fazed by the big round number facing TSL. "I can't imagine life without art and what we do, so whether it's 40 or 60 or a hundred" doesn't matter, Mussmann says. "I mean, once I fell in love with the theater, it was all-consuming — and it's all I think about. You know, I live, breathe, think, work, worry how to make it possible — to present ideas, to change minds, to open people's eyes, to have opportunities that we've shared with other people."

TSL's anniversary bash raises another question: If they're celebrating their "first" 40 years, what about the second? Bruce considers the math. "In 10 years I'll be 77, and Linda's not far behind." And she can't add up a future without her wife of almost two years, partner of 37. "If Linda's not there," she declares, "I'm not interested."